1. Field of the Invention
The invention relates to numerical control units and numerical control (NC) program creating units.
2. Description of the Related Art
As shown in Japanese Patent Application Publication Nos. S56-129912 (JP S56-129912 A) and 2008-112217 (JP 2008-112217 A), it is known to change the feed speed or the spindle speed by changing an override value of the feed speed or the spindle speed during machining in order to improve machining efficiency.
In recent years, it has been increasingly required to cut workpieces of materials with high hardness such as titanium. However, in the case of cutting high hardness materials, a tool is sometimes broken in a short time if an override value is changed as cutting steel materials. Moreover, in an NC program, a code for performing an override function is manually inserted by an operator, and is not automatically inserted.